Author Topic: Coolant glow plug effectiveness (Read 16600 times)

the caveman · « **on:** January 16, 2009, 12:54:05 pm »

Can anybody attest to how much difference those 3 glow plugs make ?
The friend that i sold my 98 TDI jetta to has been complaining that it has been taking a really long time to get heat inside. Of course he is used to big insanely thermally inefficient american V8's that get throw out heat in 2 minutes. Thing is i never found that it lacked heat and i need it to be warm. If it was really bad i would have done something about it before. Anywho this morning, since he didn't go to work i figured i would check if those glow plugs were working. Since it was just a bit too cold out to do any real work [-23oC]
i didn't disconnect them. I checked for voltage and current. Got 12 v but they aren't pulling any current, therefore none are working. I want to know if it will make much of a difference if we do change them.

jtanguay · « **Reply #1 on:** January 16, 2009, 02:58:36 pm »

Quote from: "the caveman"

Can anybody attest to how much difference those 3 glow plugs make ?
The friend that i sold my 98 TDI jetta to has been complaining that it has been taking a really long time to get heat inside. Of course he is used to big insanely thermally inefficient american V8's that get throw out heat in 2 minutes. Thing is i never found that it lacked heat and i need it to be warm. If it was really bad i would have done something about it before. Anywho this morning, since he didn't go to work i figured i would check if those glow plugs were working. Since it was just a bit too cold out to do any real work [-23oC]
i didn't disconnect them. I checked for voltage and current. Got 12 v but they aren't pulling any current, therefore none are working. I want to know if it will make much of a difference if we do change them.

i believe it would. its an interesting system that works via two relays. one relay controls two, and one relay controls the other one. this allows any combination. 1 gp (one relay), 2 gp (other relay), 3 gp (both relays) which is interesting because i thought that all three came on at the same time regardless of temp.

i'm very much considering installing this into my engine, as i don't really make heat fast enough. it's like driving a domestic car :roll: just yesterday i was driving dads other car (daewoo) and in -15C weather it took about 10 minutes of driving just to get piss warm air out of the vents. my 1.6TD would have been giving out some serious heat by then!! even my mTDI would have been warmer (beauty of VW/Audi's - they give out lots of heat despite engine not up to temperature)

madrogers · « **Reply #2 on:** January 16, 2009, 10:48:46 pm »

I am a littel confused, my vw exp has been with the old 1.6na rabbits not the newer stuff, but i am trying to see the connetion between glow plugs and cabin heat??

cyrus #1 · « **Reply #3 on:** January 16, 2009, 10:58:47 pm »

Some TDI's have 3 glow plugs located in the coolant neck on the side of the head. The idea is to heat the coolant up faster on cold mornings.

the caveman · « **Reply #4 on:** February 08, 2009, 03:22:19 pm »

So i did some testing. There was 12v going into the relay, and i checked for a signal to it from the ecu with the coolant sensor disconnected. Had a signal so i ordered a new relay [retail 185, i paid 80] . The other day i remembered that the system can be checked with the output test with Vagcom. My friend came by today [only -5oC , not too bad to work in the sun] and we did the output test. Test showed relay putting out 12 v of the relay. But i knew already that the wiring between the relay and GPs was bad, so all i did was run 3 new wires to them. Tested with output test again, 12v going all the GPs . Disconnected the coolant and intake air [according to the manual,it's intake air that the ecu uses to determine when to light the relay] temp sensors and i have 12v going but not cuurrent is being drawn. It could be the ecu is using the fuel temp as a default and not letting the relay light up or the relay is burnt and not capable to provide the current. I let my friend try it, but may have to replace the relay anyways.

jtanguay · « **Reply #5 on:** February 09, 2009, 12:20:40 am »

that is very odd that the system uses intake air temp to control the coolant glow plugs... a more effective system would be to use the actual coolant temp itself, would it not?

the caveman · « **Reply #6 on:** February 09, 2009, 09:18:12 am »

Quote from: "jtanguay"

that is very odd that the system uses intake air temp to control the coolant glow plugs... a more effective system would be to use the actual coolant temp itself, would it not?

Well that's what the workshop manual says. And like i mentioned, after replacing the wires, and disconnecting both the coolant and air temp sensors ,it still didn't work. I wouldn't be surprised if the ecu takes fuel temp into consideration as a default. I hope to get some feedback from my friend in a day or two. I still have the new relay and may have to use it after all. The system did work at least for some time because the 12 v supply and the 2 wires going from the relay had been replaced before and needed to be done again. And i'm sure it worked when i owned it.

shegel · « **Reply #7 on:** February 09, 2009, 02:15:29 pm »

on my 99.5 it does make a large difference. within 1 mile aprox of driving i have luke warm air coming out the vents. within 5 miles its up to temp.

that one mile is without even touching the temp guage

the caveman · « **Reply #8 on:** February 09, 2009, 03:57:18 pm »

That's the thing . I seem to remember having at least warm air after only few minutes. my friend is saying he has to travel about 10 kms before he gets any real heat.

Dan414 · « **Reply #9 on:** February 20, 2009, 09:25:57 pm »

Are the coolant glow plugs controlled by the glow plug relay, or is there a separate relay for them?

the caveman · « **Reply #10 on:** February 20, 2009, 10:57:27 pm »

There is a seperate relay. It's on the firewall with a glow plug fuse , 3 large gauge wires and a 3 wire connector. I'm still waiting for my friend to tell me if he has noticed a difference since i repaired the wiring. It hasn't been very cold the last week.